/Engine/Source/Developer/TextureCompressor/Public/TextureCompressorModule.h
Returns the number of mips that the given texture will generate with the given build settings, as well as the size of the top mip. Used for physical textures - not virtual textures.
static int32 GetMipCountForBuildSettings ( int32 InMip0SizeX, int32 InMip0SizeY, int32 InMip0NumSlices, int32 InExistingMipCount, const [FTextureBuildSettings](API\Developer\TextureCompressor\FTextureBuildSettings) & InBuildSettings, int32 & OutMip0SizeX, int32 & OutMip0SizeY, int32 & OutMip0NumSlices )